Convert a standard mardown file into the subset of markdown 
that can be used to generate gemtext and comparable HTML.

HEADINGS
-round markdown's six headings into gemtext's 3
    -h1 = h1
    -h2 = h3
    -h3 = h3
    -h4 = h5
    -h5 = h5
    -h6 = h5

ORDERED LISTS
-convert to plain text ordered lists

TABLES
-convert tables into ASCII art tables
    -put in ```preformatted text```
    -a certain size limit will need to be created
    -generator should throw a warning

CODE
-code highlighting should work for HTML
-use ```preformatted text``` for gemtext

LINKS
-links should be moved to a list below the paragraph they are found in
-in their place the text of the link should be kept in the paragraph
with a reference number like [1] or [22]
-the numbers should not repeat in each page

IMAGES
-handle like links